1. Field of the Invention
This invention relates to a recording and/or reproducing apparatus for recording or reproducing an optical disc under tracking servo control, and to a tracking control method for an optical disc.
2. Description of the Related Art
In an optical disc drive device, recording or reproducing data for an optical disc in general, a tracking servo loop is formed for performing loop control, in order to permit a laser light beam radiated from an optical pickup to follow accurately the track center position of the optical disc.
Specifically, the tracking servo loop is completed in the following manner in an optical disc driving device. That is, the optical disc driving device radiates a laser light beam on a track of an optical disc from the optical pickup to detect the reflected laser light bean by a photodetector, which then detects the reflected light to send a detection signal corresponding to the light volume of the reflected light to a matrix amplifier. The latter converts the detection signal to a voltage level signal, while generating tracking error signals representing the position offset components of the laser light spot with respect to the track center. The tracking error signals are phase compensated in a pre-set manner by a filter and thence supplied to a tracking driver adapted for driving a biaxial actuator adapted in turn for causing movement of the objective lens of the optical pickup. The tracking driver is responsive to the phase-compensated tracking error signals to drive the tracking coil of the biaxial actuator to cause movement of the objective lens vertically with respect to the optical axis and radially with respect to the optical disc.
The optical disc drive device completes a tracking servo loop as described above to correct the position deviation of the laser spot to cause the laser light illuminated on the optical disc to follow the track center by way of tracking control.
It should be noted that, in the conventional optical disc driving device, there are produced variations in the tracking servo loop gain, from one optical disc to another, due to a difference in the intensity of the reflected light or in an intensity distribution. In particular, since the tracking error signals are produced on the basis of push-pull signals representing the difference in reflected light volume obtained from both edges of the guide groove formed in the track, there is produced a significant difference in sensitivity due to the difference in the intensity of the reflected light or in the intensity distribution. Thus, for eliminating the variations in the loop gain, the conventional optical disc driving device detects traverse signals produced when the laser light traverses the track, such as at the time of optical disc loading or tracking pull-in, and performs calibration, etc., to assure a constant amplitude of the traversing signal to adjust the loop gain.
Meanwhile, in the conventional optical disc driving device, the loop gain for tracking servo control fluctuates due to the flexure or distortion of the recording surface, thermal changes or changes with lapse of time, even in the course of the recording/reproduction of the same optical disc. In particular, if data are continuously recorded or reproduced over a wide range of tracks of the optical disc for recording/reproducing a large quantity of data or for a prolonged time period, the risk is high that differences in reflection intensities or intensity distribution will be produced with the result that the loop gain tends to fluctuate.
Recently, with the increased capacity of the optical disc, the objective lens tends to be increased in numerical aperture (NA), while the laser light tends to be reduced in wavelength, with the result that the disc thickness is increasingly reduced. Thus, the effect of warping of the optical disc tends to be manifest, such that the reflection intensity or intensity distribution tends to be produced in the course of recording or reproduction to render the loop gain more susceptible to fluctuations.
However, since the conventional optical disc driving device detects the traverse signal to adjust the loop gain, it is necessary to interrupt the tracking servo loop transiently to adjust the loop gain. Thus, in the conventional optical disc driving device, if the loop gain fluctuates, it has not been possible to adust the loop gain in real time.
Therefore, if, in the conventional optical disc driving device, data is to be recorded or reproduced over a wide area of the optical disc for recording/reproducing a large quantity of data or for prolonged time, it has been difficult to assure tracking servo stability.
It is therefore an object of the present invention to provide an optical disc recording and/or reproducing method and apparatus and an optical disc tracking control method whereby loop gain variations in the tracking servo control can be suppressed in real-time to enable the illuminating laser light to follow the track center position accurately.
In one aspect, the present invention provides a data recording/reproducing apparatus for an optical disc, the optical disc having a recording track carrying a guide groove for causing an illuminated laser spot to follow the center position of the recording track, the guide groove being meanderingly formed in meeting with wobbling signals of a pre-set frequency, in which the apparatus includes push-pull signal detection means for detecting push-pull signals containing tracking error signals representing error components from the track center and the wobbling signals, wobbling signal detection means for detecting the wobbling signals from the push-pull signals detected by the detection means, and control means for controlling the level of at least the tracking error signals in meeting with the level of the detected wobbling signals.
In the optical disc recording and/or reproducing apparatus, the tracking error signal level is controlled responsive to the detected wobbling signal level to adjust the tracking servo loop gain.
In another aspect, the present invention provides an optical disc tracking controlling method for an optical disc, the optical disc having a recording track carrying a guide groove for causing an illuminated laser spot to follow the center position of the recording track, the guide groove being meanderingly formed in meeting with wobbling signals of a pre-set frequency, in which the method includes detecting push-pull signals containing tracking error signals representing error components from the track center and the wobbling signals, detecting the wobbling signals from the detected push-pull signals to control the level of at least the tracking error signals in meeting with the level of the detected wobbling signals, and detecting the level-controlled tracking error signals from the detected push-pull signals to control the position of a laser spot illuminated on the optical disc based on the tracking error signals.
In the optical disc recording and/or reproducing method, the tracking error signal level is controlled responsive to the detected wobbling signal level to adjust the tracking servo loop gain.
In the optical disc recording and/or reproducing apparatus and the optical disc tracking controlling method, according to the present invention, the tracking error signal level is controlled responsive to the detected wobbling signal level to control the tracking error signal level and the tracking servo loop gain.
According to the present invention, if the loop gain of the tracking servo control is varied during recording or reproduction due to flexure or distortion of the recording surface of the same optical disc, thermal changes or to changes with lapse of time, it is possible to suppress the variation in the loop gain in the tracking servo control in real time to cause the illuminated laser light to follow the center of the recording track reliably.
Moreover, according to the present invention, it is possible to suppress the loop gain variation over the entire data recording or reproducing area in case of continuous data recording or reproduction on a broad area of an optical disc, such as when recording or reproducing a large quantity of data or over an extended period of time, to cause the illuminated laser light to follow the recording track center.